Knowledge concerning phasic coronary blood flow is primarily based on measurements obtained from epicardial coronary arteries. Epicardial coronary arteries, in addition to their conduit function, have capacitance function. One effect of this capacitor would be the distortion of the phasic perfusion of the myocardium. A model that we have utilized to eliminate epicardial capacitance, but not intramyocardial capitance effects, is the measurement of phasic blood flow velocity from the septal artery and small epicardial arteries just before they penetrate in the myocardium. We can then dissect the capacitance effects of epicardial arteries from those of intramyocardial arteries. We plan to analyze the effects of coronary capacitance on intramyocardial blood flow during hemodynamic perturbations, which are reported to change the phasic nature of coronary blood flow. We also will determine if the "intramyocardial capacitor" and "epicardial capacitor" are differentially affected by vasoactive substances. Another goal is to determine if epicardial capacitive influences affect measurements of the coronary stop-flow pressure. We also plan to determine if measurements of phasic coronary venous flow will support the concept of a collapsed segment of the coronary vasculature during diastole, that is subject to modulation by vasodilators. The results of these studies should provide new insights into basic mechanisms that influence the myocardial perfusion.